Combine the butter and chocolate in a bowl and place over a hot water bath. Cook until they are melted and smooth. Remove from heat and allow to cool down for 10-15 minutes.
Stir in the sugar and mix well then add the eggs, one by one, mixing well after each addition.
Add the vanilla extract and mix.
Sift the flour with cocoa powder, salt, baking soda and baking powder. Fold it into the chocolate mixture.
Spoon the batter in a muffin tin lined with muffin papers.
Bake in the preheated oven at 350°F - 180℃ for 15-20 minutes until well risen and set in the center. Don't over bake them as they tend to dry out!